1. Field of the Invention
The present invention relates to a method and related apparatus for improving Continuous Packet Connectivity in a wireless communications system, and more particularly, to a method and related apparatus for improving a start procedure of DTX-DRX operation, for improving Continuous Packet Connectivity.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system, the Universal Mobile Telecommunications System (UMTS), has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS (Quality of Service) requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting the third generation mobile telecommunication technology, the prior art provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate.
According to the related protocol specifications, one of protocol stacks of the UMTS, access stratum (AS), can be segmented into sub-layers for different functions. The operations of the sub-layers in the AS are well known in the art, and detailed description is not given here. The Radio Resource Control (RRC) layer, a Layer 3 protocol, is the core of communications protocols related to AS and is located in radio network controllers (RNC) of the UMTS Terrestrial Radio Access Network (UTRAN) and a user equipment (UE). The RRC layer uses RRC messages to perform RRC procedures. RRC messages are formed from many information elements (IEs) used for embedding necessary information for setting, changing, or releasing protocol entities of Layer 2 and Layer 1, thereby establishing, adjusting, or canceling information exchange channels to perform data packet transportation.
For improving HSDPA and HSUPA, the 3rd Generation Partnership Project (3GPP) provides a Continuous Packet Connectivity (CPC) protocol specification, which includes features that, for UEs in CELL_DCH state, aim to significantly increase the number of packet data users for a cell, reduce the uplink noise rise and improve the achievable download capacity for VoIP.
According to the CPC protocol specification, a discontinuous transmission and discontinuous reception (DTX-DRX) operation is used to reduce power consumption when transmission between a UE and the UTRAN is decreasing. The DTX-DRX operation includes discontinuous uplink transmission (uplink DTX), discontinuous uplink reception (uplink DRX) and discontinuous downlink reception (downlink DRX). Uplink DTX is a mechanism where control signals are transmitted on the uplink control channels according to defined discontinuous patterns during the inactive state of corresponding uplink data channels, such as Enhanced Dedicated Transport Channel (E-DCH) or High Speed Physical Control Channel (HS-DPCCH), in order to maintain signal synchronization and power control loop with less control signaling. Uplink DRX is utilized for controlling the UE to transmit E-DCH in specific time interval and has to be configured with uplink DTX. Downlink DRX is configured by a Radio Network Controller (RNC) and allows the UE to restrict the downlink reception times in order to reduce power consumption. When the downlink DRX is enabled, the UE is not required to receive physical downlink channels except for several specific situations. Please note that the DTX-DRX operation is enabled only when the UE is in CELL_DCH state.
Associated configurations of the DTX-DRX operation are described as follows. If the UE receives RRC CONNECTION SETUP, ACTIVE SET UPDATE, CELL UPDATE CONFIRM, or any other reconfiguration message, the UE shall determine the value for a DTX_DRX_STATUS variable that indicates a status of the DTX-DRX operation. The DTX_DRX_STATUS variable shall be set to TRUE for starting the DTX-DRX operation only when all the following conditions are met:                1. the UE is in CELL_DCH state;        2. both variables HS_DSCH RECEPTION and E_DCH_TRANSMISSION are set to TRUE;        3. no DCH transport channel is configured;        4. a variable DTX_DRX_PARAMS is set; and        5. the UE received an IE “DTX-DRX timing information”.        
If any one of the above conditions is not met and the variable DTX_DRX_STATUS is set to TRUE, the UE shall:
1. set the variable DTX_DRX_STATUS to FALSE;
2. clear the variable DTX_DRX_PARAMS; and
3. stop the DTX-DRX operation related activities.
In summary, the UE controls start or stop of the DTX-DRX operation by setting the variable DTX_DRX_STATUS to TRUE or FALSE. On the other hand, the UE stores the content of the received IE “DTX-DRX timing information” in the variable DTX_DRX_PARAMS. The variable DTX_DRX_PARAMS includes the IE “DTX-DRX timing information” and an IE “DTX-DRX information”. The IE “DTX-DRX timing information” is used for indicating timing information of the DTX-DRX operation and comprises other IEs, such as an IE “CHOICE timing”, an IE “DTX information”, an IE “DRX information”, and so on. The UTRAN has to transmit the IE “CHOICE timing” using for selecting a timing of the DTX-DRX operation to the UE to reconfigure the timing of the DTX-DRX operation. The content of the IE “CHOICE timing” comprises “new timing” or “continue”.
Known as associated 3GPP protocols, if the UE confirms that the IE “DTX-DRX timing information” is included in a received reconfiguration message and the IE “CHOICE timing” is set to “new timing”, the UE stores the content of the IE “DTX-DRX timing information” in the variable DTX_DRX_PARAMS. At the same time, if the UE confirms that the IE “DTX-DRX information” is included in the received reconfiguration message, the UE also stores the content of the IE “DTX-DRX information” in the variable DTX_DRX_PARAMS.
In fact, if the UE confirms that the IE “CHOICE timing” is set to “new timing”, the UE can use the content of the IE “DTX-DRX timing information” and does not store it in the variable DTX_DRX_PARAMS. The UE only stores the IE “DTX-DRX information” in the variable DTX_DRX_PARAMS.
From the above, the UE starts the DTX-DRX operation only when all the above 5 conditions are met. In other words, the UE stops the DTX-DRX operation only when any one of the above 5 conditions is repealed. For example, the UE has to leave CELL_DCH state, or sets the variables HS_DSCH RECEPTION and E_DCH_TRANSMISSION to FALSE in order to stop the DTX-DRX operation after the DTX-DRX operation is enabled. In other words, the UE has to disable HSDPA and HSUPA for stopping the DTX-DRX operation. If the UE wants to keep transmission, the UE has to enter CELL_DCH state again. In addition, the variable DTX_DRX_PARAMS is set and the IE “DTX-DRX timing information” is received after the DTX-DRX operation is enabled. Therefore, it is impossible to stop the DTX-DRX operation by repealing the last two of the above 5 conditions.
In conclusion, it is difficult to stop the DTX-DRX operation by repealing any one of the above 5 conditions when the DTX-DRX operation is enabled. Therefore, transmission efficiency of CPC is decreased.